Intransigent
/ɪnˈtrænsɪdʒənt/ adjective hardRefusing to compromise or change one's position, even under pressure.
Both sides remained intransigent, and the negotiations collapsed after six hours.
Memory Trick
'In-' (not) plus 'transigent' (willing to settle, from Latin 'transigere,' to come to an agreement) — intransigent people simply won't settle.